Freezing of wellhead equipment is a common risk for oil wells and gas wells in regions that experience extremely cold winters, such as Alaska, Colorado and northern Canada. Natural gas contains hydrates, which may condense out of the gas and then solidify when temperatures are very low, particularly when the situation is aggravated by a drop in gas pressure. Unless sufficient heat is provided, or unless other means are provided for preventing condensation of hydrates, the wellhead equipment installed on a producing well to control and regulate flow of oil or gas, as the case may be, can “freeze off” and cease to function when temperatures fall below freezing (i.e., zero degrees Celsius). When this happens, valuable production is lost, and additional expense must be incurred to have skilled technicians attend at the well site to remedy the freeze-off and restore flow from the well.
U.S. Pat. No. 6,032,732, issued to Yewell on Mar. 7, 2000, discloses a wellhead heating system that circulates heated coolant, from a liquid-cooled engine driving an oil well pumper, through insulated conduit arranged as desired in thermal contact with the wellhead equipment, such that heat from the circulating coolant is transferred to the equipment. The Yewell apparatus has a serious drawback, however, in that it is applicable only at well sites where a source of heated fluid is readily available, such as where a liquid-cooled engine has been provided for one reason or another.
Other approaches to the problem have included provision of heat tracing loops circulating hot water or steam from heaters or boilers, or direct injection of antifreeze fluids such as methanol. Once again, such approaches are excessively expensive if not entirely impractical for remote well sites, because of the cost and inconvenience of maintaining a reliable source of power or fuel for the heaters or boilers, or providing injection pumps and sufficient supplies of antifreeze fluids. In fact, well-operating companies may find it less costly overall to incur occasional production losses from wellhead freeze-off at remote well locations, plus the expense of sending technicians out to remedy freeze-off situations, than to provide means for keeping the remote wellheads warm, given the cost of providing heat sources (e.g., electric power, diesel generators, or propane heaters) or antifreeze injection equipment needed to prevent freeze-off.
For the foregoing reasons, there is a need in the oil and gas industry for improved apparatus and methods for preventing freezing of wellhead equipment associated with gas wells and oil wells. In particular, there is a need for such apparatus and methods that minimize or eliminate the need for antifreeze injection, or for supplementary power or fuel.